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These were secret autonomous mobile guns that was developed by the hand of Moriarty.

The scientist who built the first three had them set to search and attack human heat signatures. They never realised their mistake.
It took a squad of heavy armoured troopers 3 hours to secure the lab. Not much remained of the scientists. Shortly after the project was abandoned.

Rumours have surfaced of a successful reactivation of the program, but none alive have seen these small silent creeping destruction machines.

Rumour also claim that they hunt in packs, have a hive mind and kills all humans indiscriminately. There is no way to confirm or deny these rumours.